Over the weekend I did smallish (5+ pounds) butt. I posted sometime on Sunday that I was astonished about how long it was taking. I'd heard that sometimes the small ones go long than the bigger ones, but this was like nothing else I've ever experienced.
After 18+ hours
I finally threw in the towel and took the thing off at just over 180 degrees. I maintained rock solid 225 grate temp throughout most of the cook. Eventually I ran into some fuel exhaustion problems and had to add some more lit lump. But I never dropped them that much for that long.
My standard dome thermometer seemed to be consistent with what I was seeing on my Guru pit thermometer. I also checked meat tems with a Polder instant read, and it too matched what I was seeing on the Guru. So bottom line, I think I was getting accurate temp readings.
So my question is have you ever seen a butt take more than 3 hours per pound to cook?
Last and not least, it turned out just fine